Sulfonate grease



' Patented Feb. 6, 1951 SULFONATE GREASE John J. Kolfenbach, somervilleand Rosemary OHalloran, Elizabeth, N. .lT., as'signors to Standard OilDevelopment Company, a corporation of Delaware Application June 28,1949, Serial No. 101,866

7 Claims.

This invention relates to improved sulfonate greases and moreparticularly to a sulfonate grease containing a mixture of the calciumand lead salts of a low molecular weight aliphatic carboxylic acid.

In the patent issued to Zimmer and Duncan, No. 2,444,970, later reissuedas 23,084, it is disclosed that a superior grease composition pro--viding lubrication both at high and low temperatures and having goodstructural stability may be obtained by combining with a minerallubricating oil a so called Werner complex formed by the conversion ofan oil-soluble sulfonate into an oil-soluble complex, using a watersoluble salt. In this patent it is taught that a sulfonate greasecombined with a metallic salt of an aliphatic carboxylic acid may bemade by reacting a polyvalent metal sulfonate, such as calciumsulfonate, with a salt containing a monovalent metal, such as sodium,potassium or lithium. There is also disclosed that polyvalent metalsulfonates may be reacted with the nitrates or acetates of similar ordissimilar polyvalent metals, such as magnesium, calcium, barium, lead,tin, etc. There is also a disclosure of the fact that excess chlorideions present in the sulfonate solution used in the manufacture of apetroleum sulfonate based grease may be removed or inactivated byincorporating sufficlent lead acetate with the potassium acetate used tocombine all the chloride ions as insoluble lead chloride. To precipitatethe maximum amount of chloride ion present in the sulfonate about 2.3%by weight of lead acetate would be needed.

It has recently been found that the presence of the calcium salt of lowmolecular weight acids in combination with metallic sulfonates impartsconsiderable extreme pressure properties to the product. This increasein the extreme pressure properties of the grease at high load pressuresis apparently due to the activation of the sulfur which is present inthe sulfonate. The formation of a metallic sulfide film, due to thepresence of the activated sulfur, is evidenced by the black film whichappears on the wear area of the testing equipment and produces anoutstanding improvement in the load carrying abilities of the grease.Greases prepared from high molecular weight sulfonates and low molecularweight acid salts show extreme pressure properties superior even tothose of greases which contain extreme pressure additives. It has nowbeen found that these extreme pressure properties may be considerablyenhanced by the substitution of a part of the calcium salt by a leadsalt.

In brief this invention comprises a lubricating grease compositioncontaining a petroleum sulfonate salt in admixture with a calcium saltand. a. lead salt of. a low molecular weight aliphatic carboxylic acid.

The oil-soluble metallic sulfonates operable in this invention may beany of the alkaline earth metallic sulfonates such as calcium, barium,or

strontium sulfonate and may be prepared by any i of the methods known inthe art. It is preferred that the molecular weights of the sulfonicacids be in the range of from about 300 to about 600, the preferredrange being a molecular weight of from 350 to 500. The amount of thesullonate present in the finished grease may range from between about0.5% by Weight for soft greases up to about 50% by weight in theextremely hard greases. However, a range of from 5 to 20% by weight ispreferred. The low molecular weight carboxylic acid which may be reactedwith the calcium or lead to form the calcium or lead salt may be aceticacid, oxalic acid, proprionic acid, or lactic acid. Of these acetic acidis the one preferred. The sum total of the mixture of the calcium andlead salts of the low molecular weight acid is 10% by weight of whichtotal 2.5% to 7.5% by weight should be the lead salt.

A series of four greases showing satisfactory structures were obtainedby combining with a petroleum sulfonate salt various percentages of leadand calcium acetate, as a thickening media. Satisfactory greases wereobtained using three parts of lead acetate to one part of calciumacetate, using one part of lead acetate to one part of calcium acetate,and when using three parts of calcium acetate to one part of leadacetate. However, when using lead acetate without admixing calciumacetate, a resinous precipitate which separated from the oil was formed.

The greases formed by combining lead acetate and calcium acetate werebetter in appearance, being almost transparent, than with the greasesprepared using calcium acetate alone, The mixture of calcium and leadacetate greases possess better B. E. C. test properties. The B. E. C.

test consists of rotating a semi-shielded bearingon a vertical shaft for20 minutes at 3500 R. P. M. The results being expressed as the percentof the original 3 gram charge lost from the bearing.

The method of manufacture of these greases and the general test andinspection results are as follows:

FORMULATION 20% of a 50% concentrate of the strontium salt of a 450molecular weight petroleum sulfonic acid was dissolved in an acidtreated coastal distillate, having a 55 SUS viscosity 210 F., at atemperature of about 150 F. A 20 aqueous solution of calcium acetat insufiicient quantity to introduce the desired amount of calcium acetatewas added and the batch partially dehydrated at 200 F. The lead acetatewa then added as a 30% solution. After the addition of the lead acetatesolution the batch was then dehydrated at 240 F. and placed in an ovenat 300 F. for 2-3 hours to finish the dehydration.

TABLE I Sulfonate greases As was stated above it has recently been foundthat the presence of the calcium salt of low molecular weight acids incombination with the metal salts of petroleum sulfonic acids inlubricating grease compositions imp-arts considerable extreme pressureproperties to the product. This very desirable result is believed to bedue to the activation of the sulfur of the sulfonate to form a metallicsulfide film which acts as a boundary lubricant on the bearing surfacesunder conditions of high load. In accordance with the present inventionthe substitution of a lead salt for a portion of the calcium saltconsiderably enhances these extreme pressure properties.

With the increase in industrial bearings having extremely smallclearances and bearing increasingly heavier loads, it has becomenecessary to develop lubricants which are capable of withstanding thesemore stringent work conditions. The development of these lubricants hasnecessitated a method of measuring in the laboratory their behaviorunder extreme conditions of high pressure and high rubbing speeds. Metalto metal contact between heavily loaded gears running at high speedsoften results in the welding together of microscopic areas of thecontacting surface. The tearing apart of such Welded points roughens thegear surface and leads to more generation of heat, further welding andtearing of the surface, and possible seizure.

The damage done to a metal surface by continued rubbing after scoring orseizure has started may be either large or small depending on theability of the lubricant to aid in quickly repolishing a damaged area.The tendency of a lubricant to minimize wear resulting from seizure is aproperty distinct from the ability to prevent seizure and provides afurther index for evaluating extreme pressure lubricants.

In order to mechanically test in the laboratory the behavior oflubricants under extreme conditions of pressure and. rubbing speeds,there has been developed a testing machine known as the Four-balltester. A controlled load is placed upon one rotating ball which issupported by three stationary balls of like characteristics. Thelubricant being tested surrounds the contact surface. Upon applicationof the load for a specific period of time under condition of load andhigh rubbing speeds, a Wear spot appears on each of the three supportingballs. These wear spots are measured under a microscope and theirdiameters are functions of the extreme pressure qualities of thelubricant used.

As the pressure applied is increased on the contact surface, a point isreached at which scoring of the wear spot begins. This point is calledthe point of incipient seizure. Up to this point of incipient seizure,the wear spot diameter is a linear function of the load applied. As thepressure or load is increased, a point is reached at which immediateseizure occurs followed by a breaking away of the seizure. Between thepoints of incipient seizure and immediate seizure the extreme pressureproperties of the lubricant are brought into play, that is, a goodlubricant will restrict the area of seizure to the minimum and aid inrepolishing the damaged area.

Using data obtained with the Four-ball tester, the Bureau of Ships haveset up a pressure wear index calculation based on the data on the pointsof incipient and immediate seizure which is a numerical measurement ofthe extreme pressure properties of lubricants. In its InterimSpecification 17L8 (INT) the Bureau has set forth conditions for thedetermination of pressure Wear index. By dividing the increase in loadbetween the point of incipient seizure and the point of immediateseizure by the difference in the squares of the wear spot diameters atthe same two points a value is obtained which is directly proportionalto the increase in pressure supported per unit area of the Wear spot.This value is designated as the pressure wear index.

In Table II below the pressure Wear indices of the greases madeaccording to this invention and the data from which these indices werecalculated are given.

TABLE II Eartreme pfiessure properties in 4-ball test 10% Sr. SulfonateGrease Plus: Wear Wear (per cent by Wt.) Load spot Load 1gpot P a a ram.rcs. Incip. 3 Imm. at Wear Seiz., gem Seiz., Imm. Index Ca(AC) PB(AC):Kg. Kg. Seiz 0. 0 10. 0 i 2. 5 7. 5 30. 0 0.38 90.0 1. O2 70 5. 0 5. 035. O 0. 34 110.0 1. 04 76 7. 5 2. 5 30. 0 0. 38 84. O 1. 16 45 10. 0 0.0 30. O 0. 38 110. 0 1.61 32 Std. E. P. Grease (Lithiu Grease plus 7.5%sulfurized sperm oils) 18.0 0.38 65.0 1.40 25 0rd. Soap Grease 35.0 0.3545.0 1. 60 4 It will be noted from an examination of this table that thepressure wear indices of the greases made according to this inventionvary from 45 to '76. These values compare very favorably with thepressure wear indices of a standard extreme pressure grease which rangefrom 15 to 25.

The single figure is a graphic illustration of the extreme pressureproperties of the grease of this invention. In the figure, the pressurewear index is plotted against the grease composition. As will be seenfrom an examination of the figure the optimum composition is onecontaining equal percentages of calcium acetate and lead acetate.However, the grease containing some 2 /2% to 10% calcium acetate andfrom 7%% to lead acetate have also excellent extreme pressureproperties. r

It will be understood that the conventional additive materials such asV. I. improvers, oxidation resisting agents, corrosion inhibitors,tackiness agents and the like, may be incorporated into the greasecompositions of this invention. The invention is not limited to solidgreases but is also applicable to fluid compositions which demandextreme pressure properties such as gear oils, cutting oils, drawingcompounds and the like.

What is claimed is:

1. A lubricating grease composition consisting essentially of a minerallubricating oil thickened to a grease consistency with from to 20% of-la strontium petroleum sulfonate formed from a sulfonic acid having amolecular weight of between 300 to 600, and about 10% by weight of amixture of the lead and calcium salts of an acid selected from the groupconsisting of low molecular weightaliphatic carboxylic acids having notmore than 6 carbon atoms said mixture containing from about 2.5% to 7.5%by weight of the calcium salts and from about 7.5% to 215% by weight ofthe lead salt.

2. A lubricating grease composition consisting essentially of a minerallubricating oil thickened to a grease consistency with from 5 to byweight of a strontium petroleum sulfonate formed from a sulfonic acidhaving a combining weight of 450 and about 10% by weight of a mixture ofequal amounts of lead acetate and calcium acetate.

3. A lubricating grease composition comprising a mineral lubricating'oil, from 10 to by weight of an alkaline earth metalpetroleum'sulfonate prepared from a sulfonic acid having a combiningweight of between 300 and 600fand about 10% by weight of a mixture ofthe .;lead and calcium salts of an acid selected from the groupconsisting of low molecular weightfali: phatic carboxylic acids havingnot more than 6 carbon atoms said mixture containing from about 2.5% to7.5% by weight of the calcium salts and 6 from about 7.5% to 2.5% byweight of the lead salt.

4. A lubricating grease composition consisting essentially of a minerallubricating oil thickened to a grease consistency with from about 5% to20% by weight of an oil-soluble metal sulfonate, and about 10% by weightof a mixture of the lead and calcium salts of an acid selected from theclass consisting of low molecular weight aliphatic carboxylic acidshaving not more than 6 carbon atoms, said mixture containing from 2.5 to7.5% by weight of the calcium salt and from 7.5 to 2.5% by weight of theleadsalt.

5. A lubricating grease composition comprising a mineral lubricatingoil, 10% of an alkaline earth metal sulfonate, and 10% of a mixture ofthe lead and calcium salts of an acid-=selected from the groupconsisting of a low molecular weight aliphatic carboxylic acid havingnot more than 6 carbon atoms, said mixture containing from 2.5 to 7.5%by weight of the calcium salt and from 7.5 to 2.5% by weight of the leadsalt.

6. A lubricating grease composition comprising of a mineral lubricatingoil, 10% of an alkaline earth salt of a sulfonic acid having a molecularweight of 450, 5% of calcium acetate, and 5 of lead acetate.

7. A lubricating grease composition comprising a mineral lubricating oilthickened to a grease consistency with 20% by weight of a mixture of 10%by weight of an alkaline earth metal sulfonate, prepared from a sulfonicacid with a molecular Weight of from 300 to 600, with 5% by weight of acalcium acetate, and 5% by weight of lead acetate,

JOHN J. KOLF'ENBACH. ROSEMARY OI-IALLORAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Name Date Zimmer et a1 July 13, 1948 Number

5. A LUBRICATING GREASE COMPOSITION COMPRISING A MINERAL LUBRICATINGOIL, 10% OF AN ALKALINE EARTH METAL SULFONATE, AND 10% OF A MIXTURE OFTHE LEAD AND CALCIUM SALTS OF AN ACID SELECTED FROM THE GROUP CONSISTINGOF A LOW MOLECULAR WEIGHT ALIPHATIC CARBOXYLIC ACID HAVING NOT MORE THAN6 CARBON ATOMS, SAID MIXTURE CONTAINING FROM 2.5 TO 7.5% BY WEIGHT OFTHE CALCIUM SALT AND FROM 7.5 TO 2.5% BY WEIGHT OF THE LEAD SALT.